Remote Sensing of Mineral Dust with MSG Infrared Channels

Abstract

Many processes have been suggested by which transported mineral dust interacts with different components of the climate system (e.g. radiation balance, atmospheric stability, convective clouds, wind direction and speed). Thus satellite monitoring of mineral dust activation and transport is needed to observe and quantify the impact of mineral dust on several components of the climate system. Remote sensing of mineral dust in the atmosphere mostly relies on measurements of reflected solar radiation and thus is often limited to regions with dark surfaces. Over vegetated or generally dark surfaces many methods are available to derive mineral dust optical depth from remote sensing data of polar orbiting or geostationary satellites. But in most cases these methods fail over bright surfaces as they are common in the desert regions, e.g. in the Sahara. Thus infrared measurements have to be used to derive dust information also over desert surfaces. The presented new method for the detection and analysis of mineral dust over land combines day- and night-time data from two infrared channels of Meteosat Second Generation (MSG). The Bi-temporal Mineral Dust Index (BMDI) uses brightness temperature differences between the 10.8[micro]m and 12.0[micro]m channels at day- and at nighttime (12 UTC and 03 UTC respectively) together with the difference in 10.8[micro]m brightness temperature between day and night. As mineral dust is quite absorptive in the 10.8[micro]m region and less in the 12.0[micro]m region, the use of brightness temperature differences between those bands is rather common to observe mineral dust from infrared measurements. As MSG offers measurements in both wavelength bands from a geostationary orbit, the combination of day- and nighttime observations into a bi-temporal dust index becomes possible. Thus a dust mask over land for further applications can be derived together with the dust index by applying additional threshold tests. Test cases of BMDI for several periods of enhanced dustiness together with one year’s data of BMDI, AERONET and Ozone Monitoring Instrument (OMI) Aerosol Index observations show good results in detecting dust plumes and estimating the atmospheric dust load. Also Model simulations with the Model of Atmospheric Transport and Chemistry (MATCH) in combination with the Dust Entrainment And Deposition (DEAD) model are compared with BMDI observations for selected dust episodes, highlighting the ability to detect and track dust plume propagation across the Sahara. In general those preliminary validation results highlight the ability of automatically detecting mineral dust plumes with BMDI. Thus BMDI allows for operational daily dust detection and monitoring of activated dust plumes on spatial resolutions down to the MSG pixel scale (3x3km² at nadir).